As technological development of mobile instruments and demands thereof are increased, a demand for batteries as an energy source is also increasing. Accordingly, extensive studies into batteries satisfying a number of requirements have been executed.
For representative examples in terms of battery morphology, an angled secondary battery and a pouch type secondary battery, which have a relatively small thickness and are thus applicable for articles such as mobile phones (also known as cellular phones), are in high demand. In terms of raw materials thereof, a lithium secondary battery, i.e., a lithium ion battery, a lithium ion polymer battery, etc., which has advantages such as high energy density, discharge voltage and/or output stability, is widely used.
Alternatively, a secondary battery may be classified in terms of types of a cathode/separator/anode structure of an electrode assembly and include, as representative examples, a jelly-roll (winding type) electrode assembly having a construction of winding a cathode and an anode while interposing a separator therebetween; a stack (laminate type) electrode assembly wherein a plurality of cathodes and anodes cut into pieces to a predetermined unit size are sequentially stacked while interposing a separator therebetween; a stack/folding electrode assembly having a construction of winding bi-cells or full cells, while interposing a separator between a cathode and an anode having a predetermined unit size, and so forth.
Recently, a pouch type battery having a construction of mounting a stack type or a stack/folding type electrode assembly in an aluminum laminate sheet has attracted considerable interest because of low production cost, light-weight, easy variations in shape, etc., and use thereof is also gradually increasing.
FIG. 1 is an exploded perspective view schematically illustrating a general structure of a conventional and typical pouch type battery.
Referring to FIG. 1, a pouch type battery 10 may have an electrode assembly 30, electrode taps 40, 50 extending from the electrode assembly 30, electrode leads 60, 70 welded to the electrode taps 40, 50, and a battery case 20 receiving the electrode assembly 30.
The electrode assembly 30 is a power generating device wherein a cathode and an anode are sequentially laminated while interposing a separator therebetween, and may have a stack type or a stack/folding type structure. The electrode taps 40, 50 may extend from each polar sheet of the electrode assembly 30, while the electrode leads 60, 70 may be electrically connected to a plurality of electrode taps 40, 50, respectively, which extend from the polar sheets, by, for example, welding. Each of the electrode leads 60, 70 may have an insulating film 80 attached to a part of each top or bottom face, in order to improve sealing to the battery case 20 while ensuring electrical insulation thereof.
The battery case 20 may provide a space to receive the electrode assembly 30, and be of a pouch type in terms of morphology thereof. For a laminate type electrode assembly 30 as shown in FIG. 1, in order to combine a plurality of cathode taps 40 and anode taps 50 with the electrode leads 60, 70, an inner top end of the battery case 20 is spaced from the electrode assembly 30.
Since secondary batteries including the foregoing pouch type battery mostly undergo activation of the battery by charge-discharge in a process of manufacturing a battery cell, gas generated during activation should be removed in order to manufacture a final battery cell and this operation may be called a ‘degassing’ operation.
However, the conventional process for manufacturing a pouch type battery as described above, entails some problems in that: considerable time is required to remove gas in a degassing operation wherein a sealed end is cut and gas is degassed, in turn increasing production costs; and the gas and excess electrolyte are not completely eliminated, in turn causing not a few failures in a sealing operation through thermal fusion.
Accordingly, there is still a high requirement for techniques to solve conventional problems described above.